Titanium dioxide and alkali metal titanates find widespread use in a variety of applications such as pigments in paint and skin care products and as photocatalysts in energy conversion and utilization. Sodium titanates can also serve as cation exchangers and have been shown to be effective materials to remove a range of cations over a wide range of pH conditions. Given the inorganic framework, sodium titanates (e.g., monosodium titanate) can withstand high radiation doses and, thus, are attractive ion exchangers to remove 90Sr and alpha-emitting radionuclides (e.g., 238,239Pu, 237Np, 235,238U) from high-activity nuclear waste solutions. Conversion of the sodium titanates to a peroxo-titanate form has been shown to increase the rate of strontium and plutonium removal, presumably by increasing the surface area and porosity.
In addition to ion exchange and photocatalytic applications, micron-sized sodium titanates and sodium peroxotitanates have been shown to serve as a therapeutic metal delivery platform. In this application, the sodium ions of monosodium titanate are exchanged for therapeutic metal ions such as Au(III), Au(I), and Pt(II). In vitro tests with the noble metal-exchanged titanates indicate suppression of the growth of cancer and bacterial cells by an unknown mechanism.
Historically, sodium titanates have been produced as fine powders, with particle sizes ranging from a few to several hundred microns using both sol-gel and hydrothermal synthetic techniques. More recently, synthetic methods have been reported that produced nanosized titanium dioxide, metal-doped titanium oxides and multi-metal titanates. Examples include sodium titanium oxide nanotubes and nanowires formed by reaction of titanium dioxide in excess sodium hydroxide at elevated temperature and pressure, sodium titanate nanofibers formed by reaction of peroxotitanic acid with excess sodium hydroxide at elevated temperature and pressure, and sodium and cesium titanate nanofibers formed by delamination of acid-exchanged micron-sized titanates. In addition, there have been studies reporting the addition of surfactants in sol-gel syntheses to control particle size growth resulting in the production of nano-size titanium dioxide, metal-doped titanium dioxides and multi-metal titanium oxides.
Typically, the kinetics of ion exchange are controlled by film diffusion or intraparticle diffusion, which are largely controlled by the particle size of the ion exchanger. As a therapeutic metal delivery platform, the particle size of the titanate material would be expected to significantly affect the nature of the interaction between the metal-exchanged titanate and the cancer and bacterial cells. Thus, what are needed in the art are methods for the synthesis of nanosized sodium titanates and sodium peroxotitanates and the nanosized products that can be formed according to such methods. Such nanosized sodium titanates could be utilized to enhance ion exchange kinetics and effective capacity in metal ion separation, enhance photochemical properties, as well as to facilitate metal delivery and cellular uptake from the titanate delivery platform.